Swimming pool water, in order to maintain it in a clear and pathogen-free condition, needs regular treatment with appropriate pool chemicals or chemical compositions. For many decades, chlorine gas (for public swimming pools, for example) and chlorine- or hypochlorite-releasing agents such as Ca(OH).sub.2 /Ca(OCL).sub.2 and trichloroisocyanuric acid or its salts (for private swimming pools) have been the favoured agents. Many devices have also come on the market which produce chlorine in the water circulation system of a pool by electrolysis, e.g. of HCL or NaCL solutions.
Despite the beneficial effects thereof in pool disinfection, the use of chlorine and chlorine-based products suffers from a number of disadvantages. The hypochlorous acid formed by hydrolysis of Cl.sub.2 is rapidly destroyed by sunlight (K. Wehrmann and F. Zobrist, Schweiz. Z. Hydrol. 20, 218, 1958). This disadvantage has led to the introduction of the trichloroisocyanurates as stabilizers.
Hypochlorous acid and chloride ions interact with organic matter from vegetable matter falling into pools, and with urine, perspiration and sun-tan oils from swimmers, to give various chlorinated products, one type of which, the chloramines, produces irritation of the eyes. Over the past decade or two these chlorinated products have been recognised as a health hazard (J. A. Beech et al., Amer. J. Public Health 70, 79, 1980). Thus the ingestion of these chlorinated hydrocarbons has been directly linked to stomach cancer, and a maximum of 100 p.p.b. has been recommended for potable water (J. A. Borchardt et. al., "Viruses and Trace Contaminants in Water and Waste Water", Ann Arbor Science, Michigan, 1977). L. Schou and H. Oedegaard (Miljoevardsserein 1, 277, 1981) have shown that this level is easily exceeded in many swimming pools, and there is the suspicion that absorption of these carcinogenic compounds through the skin, particularly with infants, may exceed tolerable levels.
Since the amounts of chlorinated hydrocarbons observed increase with the quantity of chlorine used, it is obviously desirable to reduce the application rate or dosage of chlorine or chlorine-based chemicals. Another incentive is the rising costs of these chemicals, and the fact that chlorine, an oxidising agent, reacts with dyes, resulting in discoloration, and eventually bleaching, of swimwear. They also attack cotton and elasticized materials in swimwear and the vinyl liners of pools. Furthermore, since chlorine is only effective over a narrow pH range, the use of chlorine in a swimming pool requires regular pH-corrective steps.
To reduce the amount of chlorine or chlorine-based chemicals needed to maintain swimming pools in a clear and substantially pathogen-free state, many variants of chemical compositions have been proposed and introduced into the market during the past two or three decades. These act mainly to destroy and/or inhibit the growth of algae and bacteria, the destruction of algae and bacteria being otherwise responsible for a major part of the consumption of chlorine. (It is to be noted, however, that the use of chlorine or chlorine-based chemicals cannot, in general, be dispensed with entirely, for the destruction of viruses and certain other pathogens still requires the use of a strong oxidising agent, for which chlorine is still regarded as the most efficient and cost-effective, and the safest.)
These compositions generally incorporate polymeric compounds containing quaternary ammonium compounds (for example, WSCP.RTM. of Buckman Laboratories, Michigan, USA, the chemical composition of which is given as poly [oxyethylene (dimethylimino)ethylene(dimethylimino)ethylene dichloride]) and/or heavy metal ions such as Cu.sup.2+, Ag.sup.+, Zn.sup.2+, Sn.sup.2+ /Sn.sup.4+, Ni.sup.2+ and Hg.sup.2+, preference being give to Cu.sup.2 + and Ag.sup.+. Other compositions (e.g. South African Patent 78/2234 to D. M. Rice) contain a Cu.sup.2+ salt and potassium iodide, which react in water to give free iodine. It is believed that the cuprous iodide produced in the reaction is reoxidised by the dissolved oxygen in the water to Cu.sup.2+, which will then reoxidise the iodide ions formed in the disinfectant action of the I.sub.2. The Cu.sup.2+ ions also act as an algicide.
Cu.sup.2+ and Ag.sup.+ and other ions with bactericidal and algicidal properties may for example be continuously generated in a pool by electrolysis using Ag/Cu sacrificial electrodes, or by the use of sparingly soluble salts. Soluble salts may also be administered by dosing devices.
The use of particularly Cu.sup.2+ and Ag.sup.+ has a number of advantages, including the low concentrations required, the provision of a long-lasting residual effect, easy handling, their low toxicity and tastelessness at the concentrations used, and the fact that sunlight has only a minor effect on their action.
However, they suffer from a number of disadvantages:
(a) They tend to give rise to a slight turbidity. PA0 (b) The presence of appreciable concentrations of chloride and sulphate ions in the pool water limits their effectiveness. PA0 (c) The metal ions have a tendency to undergo precipitation, leading particularly to the staining of the pool walls. PA0 (d) The metal ions tend to plate out on the iron metal parts of the filtration and circulation equipment, with the concomitant formation of a fine, red-brown precipitate of ferric hydroxide, particularly when Cu.sup.2+ is used in the highest concentration ranges. PA0 I. a mixture of active ingredients comprising by weight PA0 II. a copper reactivator means, comprising solid copper, PA0 III. the composition being a solid form suitable for placing in a dispenser having water pervious walls. PA0 from about 78 to about 83 percent, preferably 80 to 81 percent of copper sulphate (as CuSo.sub.4 .multidot.5H.sub.2 O), PA0 from about 0.08 to about 0.12 percent, of silver nitrate, preferably about 0.10 percent, PA0 from about 1.0 to about 1.4 percent, preferably about 1.2 percent, of sodium gluconate, PA0 from about 1.0 to about 1.4 percent, perferably about 1.2 percent, of zinc chloride or zinc sulphate (as ZnSO.sub.4 .multidot.7H.sub.2 O), PA0 from about 16.4 to about 9.6 percent, preferably about 13 percent, of water, and PA0 from about 3.5 to about 4.5 percent, preferably about 4 percent, of the complexone, preferably the tetrasodium salt of ethylenediaminetetraacetic acid. PA0 (a) placing the entire water component in a suitable container, and heating to boiling; PA0 (b) while boiling, adding the entire sodium gluconate and zinc sulphate or zinc chloride components to the boiling water, and agitating to dissolve; PA0 (c) with boiling and agitating, adding a portion of the copper sulphate and the entire component of silver nitrate, followed by a portion of the complexone; PA0 (d) with boiling and agitating, adding alternately and successively further portions of copper sulphate and a complexone, until the entire copper sulphate and complexone components have been added and dispersed and/or dissolved; and PA0 (e) pouring the resulting paste into suitable molds, and allowing the paste to solidify.
A composition used on the South African market under the trade name "Pool Wizard" since about 1983 has been successful in reducing the pool chlorine dosage. This solid composition comprises copper sulphate, silver nitrate, zinc sulphate and sodium gluconate, cast over a coil of copper wire, all provided in a small cage-like basket, serving as a dispenser, placed in the leaf trap of a pool circulation system. The solid dissolves up in the circulation water within about 30 minutes. The action of one such unit of the composition is claimed to last for 9 to 12 months, and to reduce the chlorine dosing requirement immediately by 50 percent, with a gradual further reduction of up to a total of 75 percent.
However, this composition still suffers from the disadvantages (c) and (d) enumerated above, and many complaints have been received by the manufacturers, with which the present inventor and applicant is associated, of unsightly stains forming on the walls of pools treated with this composition. The formation of a turbidity also presents problems.
There is therefore a need to improve compositions of the type containing particularly Cu.sup.2+ as one of the major bacterides/algicides, to eliminate the problems due to pool-wall staining and the disadvantages described under (d) above.
Another problem that has been encountered in the compounding of compositions for swimming pool treatment comprising heavy metal ions, especially when using unskilled staff, is the frothing of the mixture and/or the formation of black deposits (which do not readily redissolve) when the ingredients are mixed together.